4-Pyridoxolactonase from a symbiotic nitrogen-fixing bacterium Mesorhizobium loti: Cloning, expression, and characterization

4-Pyridoxolactonase is involved in the degradation pathway for pyridoxine, a free form of vitamin B6. The gene (mlr6805) encoding the putative 4-pyridoxolactonase of nitrogen fixing symbiotic microorganism Mesorhizobium loti MAFF303099 has been identified based on the genome database. The gene was cloned and overexpressed in a cotransformant Escherichia coli cell. The recombinant enzyme was dimeric protein and contained one mole of Zn2+ per mole of subunit. The enzyme showed about 30% identity with various N-acylhomoserine lactone lactonases and metallo-β-lactamases. The phylogram made with ClustalW shows that 4-pyridoxolactonase makes a cluster with Agrobacterium tumefaciens acyl-homoserine lactone lactonase. The alignment of amino acid sequences suggests that 4-pyridoxolactonase has three histidine residues probably involved in binding of Zn2+.